Altitude control system

ABSTRACT

A system for an unmanned aerial vehicle can include an altitude control system 320, which further includes a compressor assembly 400, a valve assembly 500, and an electronics control assembly 600. The compressor assembly may include a compressor housing 410 that includes a compressor inlet 402, an outlet 202, and a cavity 414 extending therethrough and joining the inlet to the outlet. A diffuser 408 may be coupled to the compressor housing. A motor housing 407 may be disposed within the central cavity at the inlet of the compressor housing, and a compressor motor 406 may be disposed within the motor housing. An impeller 412 disposed within the compressor housing may be coupled to a driveshaft 444 for rotation therewith. The valve assembly may be coupled to an opening 416 of the compressor inlet. The valve head 502 may be configured to move into and away from the inlet opening so as to change a size of the circumferential area of the inlet opening.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/US2019/037717, filed Jun. 18, 2019, which application is acontinuation in part of U.S. application Ser. No. 16/012,146 filed onJun. 19, 2018, the disclosures of which are hereby incorporated hereinby reference. International Application No. PCT/US2019/037717, filedJun. 18, 2019, also claims the benefit of the filing date of U.S.Provisional Application No. 62/782,137 filed on Dec. 19, 2018, thedisclosure of which is hereby incorporated herein by reference. Thepresent application also claims the benefit of the filing date of U.S.Provisional Application No. 62/782,137 filed on Dec. 19, 2018.

BACKGROUND

Unmanned aerial vehicles, such as balloons, may operate at substantialaltitudes. Such vehicles may operate within the Earth's stratosphere,having favorably low wind speeds at an altitude between 18 and 25 km(11-15 mi). Wind speed and wind direction vary at certain altitudes,allowing unmanned vehicles to rely on the wind speed and wind directionalone for navigation, without the need for additional propulsion means.Unmanned vehicles must therefore increase or decrease their altitude tochange course or to increase speed.

BRIEF SUMMARY

Aspects of the present disclosure are advantageous for high altitudeballoon systems. For instance, one aspect of the disclosure provides asystem that includes an altitude control system for an unmanned aerialvehicle. The altitude control system further includes a compressorassembly. The compressor assembly includes a compressor housing, adiffuser coupled to the compressor housing, a motor and motor housingand an impeller. The compressor housing can include an inlet, anentrance to the inlet, an outlet, and a central cavity extendingtherethrough and joining the inlet to the outlet. The motor housing maybe disposed within the central cavity within the inlet of the compressorhousing. The motor can be disposed within the motor housing. Theimpeller may be disposed at an outlet of the compressor housing, withthe impeller coupled to a driveshaft for rotation therewith. Theimpeller may overlie the motor housing such that the motor housing ispositioned between the impeller and the entrance to the inlet.

In one example, an interior surface of the compressor housing may extendaround the central cavity. The motor housing may be spaced away from theinterior surface, such that air may flow around the motor housing todissipate heat generated by the motor.

In another example, the compressor housing can include a firstcompressor housing that has a first cavity, a second compressor housingthat includes a second cavity aligned with the first cavity. The centralcavity may be comprised of the first and second central cavities. In analternative example, the compressor housing may be a monolithic housing.

In yet another example, the diffuser can include a first lower portionextending from the outlet of the compressor housing and a second upperportion coupled to the compressor housing. The first lower portion andthe second upper portion may be spaced apart from one another so as toform a lateral opening therebetween.

In another example of this aspect, the lateral opening may be connectedto the central cavity so as to allow air to pass through both thecentral cavity and the lateral opening.

In another example, the compressor assembly can include a mountingstructure configured to couple the motor housing to the inlet of thecompressor housing. The mounting structure can be thermally coupled withthe motor to dissipate heat generated by the motor.

In another example of this aspect, a compressor assembly can furtherincludes a radial cavity that extends from the central cavity in adirection radial to the central cavity.

In another example, the system further includes an outer envelope thatcan be configured to retain a lift gas therein and an inner envelope maybe disposed within the outer envelope. The inner envelope can beconfigured to retain ballast gas therein and the compressor assembly mayregulate an amount of air within the inner envelope. Alternatively, theouter envelope may be configured to retail a ballast gas therein, and aninner envelope disposed within the outer envelope may be configured toretain a lift gas therein. The compressor assembly regulates an amountof air within the outer envelope.

In another example, the compressor housing may be formed of at least oneof brass or stainless steel. The compressor housing may additionally becoated with an electrically-conductive conversion coating to inhibitsparking.

In still another example of this aspect, the motor housing can define abore configured to receive the driveshaft.

In another example, the system can further include an electronic controlsystem that is configured to control the altitude control system. Theelectronic control system can control an amount of air the compressorassembly sends to the inner envelope, which is configured to retainballast gas therein.

In yet another example, the system can further include a valve assemblythat is coupled to the inlet. The valve assembly may be configured toregulate an amount of air entering into the entrance of the inlet. Avalve head can be sized to fit within and fully occupy an area of theentrance. The valve head may be configured to move between a first fullyextended position within the entrance and a second retracted positionaway from the inlet opening.

In another example of this aspect, when the valve head is in the firstfully extended position, the valve head can be configured to occupy anentire area of the entrance and thereby prohibit a free flow of contentsinto and out of the inlet.

According to another aspect of the disclosure, a system includes analtitude control system for an unmanned aerial vehicle that furtherincludes a compressor assembly and an envelope configured to retain aballast gas therein. The compressor assembly includes a compressorhousing, a rotating shaft assembly, an axially movable bearing carrier,a motor, a motor and a biasing element. The compressor housing may becomprised of a first material having a first coefficient of thermalexpansion (“CTE”). The rotating shaft assembly may be coupled to thecompressor housing. The rotating shaft assembly may further include adriveshaft comprised of a second material having a second CTE and abearing assembly coupled to the driveshaft. The bearing assembly canfurther include an interior race extending around the driveshaft and adistal race extending around and spaced apart from the interior ring.The axially movable bearing carrier may house the bearing assembly. Thebearing carrier can include a first upper portion, a second lowerportion, and an intermediate projection therebetween, as well as a motorand a biasing element. The motor can be coupled to the rotating shaftassembly and the biasing element may be coupled to the bearing carrier.The rotating shaft assembly can be configured to bias the bearingcarrier toward the bearing assembly so as to preload the bearingassembly. The compressor assembly may be configured to regulate anamount of air within the envelope. The first CTE and the second CTE canbe different such that the first material is configured to expand at arate that is different than the second material as ambient temperaturechanges.

In one example, the biasing element may be configured to bias thebearing carrier and the bearing carrier may be configured to move thedistal ring of the bearing assembly in an axial direction.

In another example, a motor housing may house the rotating shaftassembly, spring, and motor.

In still another example, the bearing assembly may be positioned withinthe first upper portion and the bearing assembly may overlie a topsurface of the intermediate projection. The biasing element can bepositioned in the second lower portion of the bearing carrier, such thatthe biasing element is arranged to apply a force to a bottom surface ofthe intermediate projection opposite the top surface.

In yet another example, the biasing element can be a spring and may beselected from a group consisting of a helical spring, a wave spring, anda conical spring washer.

In still another example, the bearing assembly can further include aplurality of ball bearings positioned between the interior and distalraces.

In another example, an electronic control system can be configured tocontrol the altitude control system. The electronic control system candetermine the amount of air the compressor assembly provides to theenvelope.

In another example, the compressor assembly can further include an inletthat extends through the compressor assembly. The system can furthercomprise a valve assembly that is coupled to the inlet. The valveassembly may be configured to regulate the amount of air entering intothe inlet. The valve assembly can further include a valve head sized tofit within and fully occupy an area of an entrance to the inlet. Thevalve head can be configured to move between a first fully extendedposition within the entrance and a second retracted position away fromthe inlet opening. When the valve head is in the first fully extendedposition, the valve head can be configured to occupy an entire area ofthe entrance, thereby prohibiting a free flow of contents into and outof the inlet.

Other aspects of the disclosure provide for a system includes analtitude control system for an unmanned aerial vehicle. The altitudecontrol system can further include a compressor assembly. The compressorassembly includes a compressor housing, a rotating driveshaft, a bearingassembly, and a preloading mechanism. The compressor housing can becomprised of a first material that has a first coefficient of thermalexpansion (“CTE”). The rotating driveshaft may be coupled to thecompressor housing and include a second material having a second CTE.The bearing assembly can be coupled to the driveshaft. The bearingassembly can include an interior race extending around the driveshaftand a distal race extending around and spaced apart from the interiorrace by ball bearings that re positioned between the interior and distalraces. The preloading mechanism can be configured to dynamicallycompensate for differences in the first CTE and second CTE throughout aflight of the unmanned aerial vehicle by continually changing apreloading force applied to the bearing assembly.

In one example, the preloading mechanism can further include a movablebearing carrier and a spring. The movable bearing carrier may underliethe bearing assembly and be movable along an axis parallel to therotating driveshaft. The spring may be configured to bias the bearingcarrier towards the bearing assembly. In a specific example, when thespring biases the bearing carrier, the bearing carrier is configured tomove the distal race of the bearing assembly.

In another example, the bearing carrier can include a first upperportion, a second lower portion, and an intermediate projectiontherebetween. The bearing assembly may be positioned within the firstupper portion and overlie a top surface of the intermediate projection.The spring may be positioned within the second lower portion of thebearing carrier, such that when the spring biases the bearing carrier,the spring is arranged to apply a force to a bottom surface of theintermediate projection opposite the top surface. The spring may beselected from a group consisting of a helical spring, a wave spring, anda conical spring washer.

In another example, the system can further include an envelope that isconfigured to retain ballast gas therein. The compressor assembly canregulate an amount of air within the envelope.

In yet another example, the compressor assembly can further include amotor housing that is disposed within an inlet of the compressorassembly, and an impeller overlying the motor housing.

Other aspects of the disclosure provide for a system that includes analtitude control system for an unmanned aerial vehicle. The altitudecontrol system further includes an inlet opening and a valve system. Theinlet opening is an opening to an interior portion of the unmannedaerial vehicle. The inlet opening has a circumferential area. The valveassembly can be coupled to the inlet opening and further includes avalve head, a driveshaft, and a motor assembly. The valve head can beconfigured to move into and away from the inlet opening so as to changea size of the circumferential area of the inlet opening. The driveshaftmay be coupled to the valve head at a first end. The motor assembly maybe coupled to a second end of the driveshaft. The valve head may beconfigured to move between a first fully extended position within theinlet opening and a second retracted position away from the inletopening. When the valve head is in the first fully extended position,the valve head can be arranged to occupy an entire circumferential areaof the inlet opening thereby prohibiting free flow of contents into andout of the inlet opening.

In one example, the inlet opening may be an inlet opening of an aircompressor assembly. The air compressor may include a mixed flowcompressor. Alternatively, the inlet opening can be an inlet opening toa base plate of a balloon.

In another example, mounting stanchions may be used to join the valveassembly to the inlet opening.

In yet another example, the valve assembly can further include a sealextending around an outer surface of the valve head. The seal may bearranged to form an air-tight seal between the valve head and the inletopening when the valve head is fully extended within the inlet opening.The seal can be an energized seal that includes a jacket materialpartially enclosing a spring material.

In another example, the motor assembly can further include a motor and amotor housing and the altitude control system can further include acoupler configured to couple the motor to the driveshaft, a jam nutoverlying the coupler, and a bearing assembly disposed between the motorcoupler and the jam nut. The motor housing can define a bore that isconfigured to receive the driveshaft of the motor therethrough.

In another example, the motor housing can further include an explosionproof shaft seal disposed in the bore and mounted on the driveshaft ofthe motor. The motor housing can define an aperture configured toreceive cables therethrough. The motor housing can further include anexplosion proof seal disposed in the aperture. The motor housing canfurther include a flame arrestor.

In still another example, the system can further include an electronicscontrol assembly that further includes a circuit board. The circuitboard can further include a processor configured to control thecompressor assembly. The circuit board of the electronics controlassembly can also be hermetically sealed. The electronics controlassembly can include a current sensor configured to measure leakage incurrent. The current sensor can be electrically coupled to theprocessor.

In yet another example, the system can further include an envelopeconfigured to retain a ballast gas therein and a compressor assemblyconfigured to regulate an amount of air within the envelope.

Other aspects of the disclosure provide a system for an unmanned aerialvehicle. The system can include an altitude control system that includesa compressor assembly and a valve assembly. The compressor assemblyincludes a compressor housing, a diffuser, a motor housing, a motor, andan impeller. The compressor housing that including an inlet, an outlet,and a central cavity that extends therethrough. The compressor housingjoins the inlet to the outlet. A diffuser may be coupled to thecompressor housing. The motor housing may be disposed within the centralcavity at the inlet of the compressor housing. The motor may be disposedwithin the motor housing. The impeller may be disposed within thecompressor housing and coupled to a driveshaft for rotation therewith.The valve assembly may be coupled to an inlet opening of the inlet ofthe compressor. The valve assembly may include a valve head, a valvedriveshaft, and a motor coupled to a second end of the driveshaft. Thevalve head may be configured to move into and away from the inletopening so as to change a size of a circumferential area of the inletopening. The valve driveshaft may be coupled to the valve head at afirst end. The motor assembly may be coupled to a second end of thevalve driveshaft. The valve head may be configured to move between afirst fully extended position within the inlet opening and a secondretracted position away from the inlet opening. When the valve head isin the first fully extended position, the valve head may be configuredto occupy an entire circumferential area of the inlet opening andthereby prohibit free flow of contents into and out of the inletopening.

In one example, compressor assembly can further include a rotating shaftassembly, a motor coupled to the rotating shaft assembly and a biasingelement. The rotating shaft assembly can further include the compressordriveshaft, as well as a bearing assembly and a movable bearing carrier.The bearing assembly may be coupled to the driveshaft and include aninterior race extending around the driveshaft and a distal raceextending around and spaced apart from the interior race. The movablebearing carrier can house the bearing assembly. A motor can be coupledto the rotating shaft assembly. The biasing element can be coupled tothe bearing carrier and be configured to bias the bearing carrier so asto preload the bearing assembly.

In another example, the system can further include an envelope and acompressor assembly. The envelope can be configured to retain a ballastgas therein and the compressor assembly can be configured to regulate anamount of air within the envelope.

In yet another example, the altitude control system can include anelectronics control assembly that includes a circuit board that furtherincludes a processor configured to control the compressor assembly. Thecircuit board of the electronics control assembly is hermeticallysealed. The electronics control assembly may include a current sensorconfigured to measure leakage in current. The current sensor can beelectrically coupled to the processor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a system in accordance with aspects ofthe present disclosure.

FIG. 2 is an example of a balloon in accordance with aspects of thepresent disclosure.

FIG. 3 is an example of a balloon in flight in accordance with aspectsof the disclosure.

FIG. 4 is an example altitude control system in accordance with aspectsof the disclosure.

FIG. 5 is a mixed flow air compressor with inlet mounted motor inaccordance with aspects of the disclosure.

FIG. 6 is cross-sectional view taken along line A-A of FIG. 5.

FIG. 7 is a perspective view of the example motor housing of FIG. 6 inaccordance with aspects of the disclosure.

FIG. 8 is a cross-sectional view taken along line B-B of FIG. 7;

FIG. 9 is a chart showing the efficiency of a compressor assemblyaccording to aspects of the disclosure as compared to a prior compressorassembly.

FIG. 10 is a cross-sectional view taken along line C-C of FIG. 7.

FIG. 11 is an example of a valve assembly of an example altitude controlsystem according to aspects of the disclosure.

FIG. 12 is a cross-sectional view taken along line D-D of the examplevalve assembly of FIG. 11 disposed within an example inlet, according toaspects of the disclosure.

FIG. 13 is a view of the example valve assembly in a closed position,

FIG. 13A is a cross-sectional view of the example valve assemblydisposed within an example inlet taken along cross line E-E of FIG. 13.

FIG. 14 is an example seal of the example valve assembly according toaspects of the disclosure.

FIG. 15 is an example control electronic assembly according to aspectsof the disclosure.

FIG. 16 is a schematic cross-sectional view showing slot linersaccording to an aspect of the disclosure.

DETAILED DESCRIPTION

A. Overview

An altitude control system can be implemented within an unmanned aerialvehicle, such as balloons used in the stratosphere. According to aspectsof the disclosure, an altitude control system for an unmanned aerialvehicle, such as balloons (including stratospheric balloons that can beused in the stratosphere), airships, etc. can include three primarysub-assemblies: (1) air compressor assembly; (2) valve assembly; and (3)electronics control assembly. These subassemblies cooperate to increaseor decrease the altitude of the unmanned aerial vehicle, which canchange the course of the balloon. In alternative examples, one or moredifferent subassemblies may be substituted. Additionally, each of thesubassemblies may be individually and independently used in other typesof applications outside of unmanned aerial vehicles and/or stratosphericballooning technology.

1. Overview: Improved Air Compressor for Altitude Control System

Axial and centrifugal air compressors are two types of air compressorsimplemented within turbomachines for use with altitude control systemsfor both manned and unmanned vehicles. Axial compressors provide lowpressure and high inlet/outlet air velocity and centrifugal aircompressors provide high pressure and medium inlet/outlet air velocity.Axial air compressors are also limited to the extent that they arecapable of only achieving a modest pressure rise. The drawback to theuse of centrifugal air compressors, however, is the creation of wasteheat, stagnated air, and overall inefficient compression of air.

Mixed flow compressors present another type of air compressor. Whiletraditional mixed flow compressors aim to combine the advantages ofaxial and centrifugal flow, the resulting combination is an aircompressor that provides only moderate pressure and low inlet/outlet airvelocity. The use of a traditional mixed flow compressor in anyindustrial application is therefore undesired due to its inability toprovide either high air velocity or high compression ratio.

To address these issues, an air compressor assembly for use with thealtitude control system of an unmanned aerial vehicle can be used tochange the amount of air within an envelope by creating an increase ordecrease in the amount of air provided to the balloon. In one example, amixed flow compressor utilizes an inlet-mounted motor. This mixed flowcompressor design can allow for the use of a high power density motor todrive the air compressor by counteracting high levels of heat generatedby the motor and causing motor failure because the motor is placed inthe flow of cold air through the inlet of the device, cooling the motor.Furthermore, because unmanned aerial vehicles may primarily rely uponwind currents for movement, there is no need for an air compressor toproduce high pressure or high velocity to move the balloon at highspeeds. Mixed flow compressor designs in the configuration disclosedherein therefore provide an optimized solution for inclusion of anefficient air compressor assembly within a stratospheric balloon.

The mixed flow compressor assembly can include a diffuser, a compressorhousing, including first and secondary compressor housings, a motormounted within the inlet of the first compressor housing, and animpeller. When assembled together, these components define a centralcavity or plenum of the mixed flow compressor. An opening at one end ofthe compressor housing may form an intake at the inlet end of thecompressor assembly. The compressor housing defines a cavitytherethrough to enable air or other fluid to flow through the compressorhousing.

The primary compressor housing may be coupled to a diffuser. Thesecondary compressor housing may be positioned between the primarycompressor housing the diffuser. The diffuser, primary compressorhousing, and motor can be attached to the secondary compressor housing.The diffuser may be configured to convert the mechanical work done by amotor and an impeller of the compressor back into potential energy inthe form of air pressure. The diffuser may efficiently convert thekinetic energy of the compressed, flowing air into higher pressure,static air in an envelope of the balloon.

The impeller draws air from the environment surrounding the altitudecontrol system into the inlet of the compressor assembly and through thecentral plenum. The air drawn from the environment may be extremely coldand flows through the inlet into the central plenum and around themotor. This may cool down the motor and dissipate heat generated by themotor to prevent overheating. Positioning the motor within the inlet, asopposed to an outlet end or elsewhere in the device, enables use of amotor having high power density.

The mixed flow compressor assembly design may combine axial and radialcomponents to produce a diagonal airflow compressor stage. In thepresent design, the exit mean radius of the airflow can be greater thanat the inlet, like in a centrifugal design, but the flow will exit thecompressor in an axial rather than radial direction.

The features of the disclosed mixed flow compressor with the motorpositioned at the inlet allows for a compressor assembly that issignificantly more efficient than prior versions. This is due in part tothe cooling provided by the motor at the inlet end of the compressor.Such design allows for twice the ability to steer the unmanned aerialvehicle using half the power utilized in prior designs, and forsignificantly reduced mass.

2. Overview: Dynamic Axial Preloading Assembly for Air CompressorBearing Assembly of Altitude Control System

When implementing an altitude control system in a balloon, weight isparamount. The altitude control system must be made from durablematerials capable of withstanding extreme temperature changes and harshenvironmental conditions. A thermally conductive material may be desiredto help cool down the motor. Moreover, to ensure that the weight of thealtitude control system does not adversely affect balloon flight andlift, the selected materials cannot be too heavy. The housings and themajority of the components of the altitude control system are thereforetypically comprised of aluminum, which is thermally conductive. Aluminumhas the additional advantages of being a light-weight material,naturally corrosion resistant, ductile, and capable of maintaining thestructure of the housings. Moreover, aluminum is approximately one-thirdthe weight of steel, such that aluminum parts can be made thicker toincrease their strength, while still allowing for an overall reductionin weight of the vehicle.

To enable manufacture of an altitude control system small enough to beused with an envelope of an unmanned aerial vehicle, a driveshaft madeof steel can be implemented within the compressor assembly of thealtitude control system. A driveshaft made from a lighter materialhaving a coefficient of thermal expansion that can match the remainderof the altitude control system, such as aluminum, would have anexcessive diameter necessary to provide the strength and stiffness ofsteel and would not be practical to employ. The result is an altitudecontrol system with a shaft that expands and contracts at a differentrate than the majority of the altitude control system.

In many instances, the bearings of the bearing assemblies becomeunloaded, which causes catastrophic failure. The mismatched coefficientsof thermal expansion of steel and aluminum coupled with backpressurefrom within the balloon envelope, and the extreme temperature changescaused by the surrounding environment at high altitudes, may lead tofailure of the altitude control system. Similarly, because the altitudecontrol system must operate at very high rotational velocities, criticalshaft rotor dynamic mode often occurs inside the operating range of thedevice and also leads to catastrophic failure.

The unexpected temperature changes that cause expansion and contractionof these components at different rates, as well as the advance andunknown temperature changes the altitude control system will encounterthroughout the duration of its flight, make it difficult to predict andprovide for a static preloading force that can be applied to the bearingassembly and that will be an appropriate force for the lifetime of thedevice. The solution to address these issues has been to carefullymachining the compressor and shaft assembly components to specifictolerances to accommodate expansion and contraction of these materials.This procedure is time consuming, costly, and complex, both in terms ofdetermining the appropriate tolerances, as well as machining componentswithin the predefined tolerances. Moreover, such procedure provides manypossibilities for failure since the tolerances must be accuratelydetermined for each individual component, and the failure at any one ofthese components will result in overall failure of the altitude controlsystem. Moreover, tolerancing components of the altitude control systemis limited to the exact ranges of tolerances provided; anything outsideof this predetermined tolerance will result in failure of the altitudecontrol system.

To address such failures, a dynamic axial preloading assembly that canbe integrated inside the motor housing of a device, such as an aircompressor, and that can maintain bearing preload of a rotating shaftassembly in order to achieve a long-lasting device when ongoingmaintenance cannot be performed may be used. Bearing preload can becritical to extend the life of the rotating shaft assembly of a motorwithin the unmanned aerial vehicle, which must fly for the duration ofits life without returning to the ground. In accordance with aspects ofthe disclosure, radial support, in combination with dynamic axialpreload can address shortcomings related to backpressure from within anenvelope, mismatched coefficient of thermal expansion, and extremetemperature changes caused by the environment surrounding the aerialdevice. Such aspects help to eliminate the manufacture of individualcomponents that separately address these shortcomings.

An example altitude control system may include a dynamic axialpreloading assembly for the rotating shaft assembly of an air compressorof an unmanned aerial vehicle. The rotating shaft assembly can include arotating driveshaft coupled at one end to the impeller, as well as abearing assembly that is positioned within a bearing housing or carrier.The preloading assembly can include a bearing carrier and a biasingelement to exert force on the bearing carrier, so as to “float” thebearing assembly that supports the shaft assembly.

The bearing carrier can be configured to move in an axial directionalong the axis of the driveshaft due to the spring force exerted uponthe bearing carrier. The biasing element may be any element configuredto exert a force on the bearing carrier. The biasing element may bepreloaded and can be adjusted to exert a preloading force on thebearing.

When in use, as the environment changes, the biasing element may presson the bearing carrier and the bearing assembly to keep the bearingassembly preloaded and engaged with an appropriate preloading force.This can help to prevent the catastrophic failure that would result fromunloading the bearing at high speed. The biasing element thereforecompensates for changes in atmosphere, backpressure, temperature, etc.that would otherwise affect the bearing assembly.

Thus, the features disclosed herein, provide for an altitude controlsystem that utilizes an air compressor assembly with dynamic axialpreloading for use with an unmanned aerial aircraft. Such featuresaddress the shortcomings associated with failure of the rotating shaftassembly of a motor within the unmanned aerial vehicle due to externalforces to the bearing assembly caused by, for example, back pressurefrom within an envelope of the balloon, mismatched coefficient ofthermal expansion between the steel driveshaft and aluminum housing, andlarge temperature changes caused by the environment surrounding a devicewithin the unmanned aerial vehicle. In this regard, the featuresdisclosed eliminate the need to manufacture individual components thatseparately address these shortcomings.

3. Overview: Valve Assembly for Altitude Control System

Valve assemblies can play an integral role in an altitude control systemof unmanned aerial vehicles. The valve assembly can be used to regulate,direct, or control the flow of air by opening, closing, or partiallyobstructing a particular opening or passageway to an envelope of theunmanned aerial vehicle. Valve assemblies implemented as part of analtitude control system must operate in extreme conditions. Long flightsand extreme temperature changes are encountered by the altitude controlsystem and the valve assemblies of these systems. Known valve assemblydesigns require periodic maintenance, making such valves undesirable foruse with long flights. Most known valve assemblies are capable ofoperating in only two positions: a completely open position or acompletely closed position. Additionally, valve assemblies that providea good seal are extremely heavy, and therefore not desired for use inconnection with aerial vehicles, such as balloon assemblies. Finally,known valve assemblies are typically complex structures with multipleparts, some on the order of 100 parts.

To address these shortcomings, a valve assembly of the altitude controlsystem can regulate, direct or controls the free flow of air by opening,closing, or partially obstructing various passageways may be used. Thevalve assembly can be mounted to the inlet of an air compressor, such asthe mixed flow air compressor described above, and the bell-mouth-shapedinlet serves as the structural connection of the valve to the broaderaltitude control system and unmanned aerial vehicle. The features of thedisclosed valve assembly can allow for effective operation of the valveassembly at high altitudes and allows for the contents of an envelope toremain sealed within the envelope at extremely low air temperatures.Additionally, the features of the disclosed valve allow for alightweight valve assembly that requires little to no maintenance duringflight. Additionally, such valve assembly can be made significantly lesscomplex to manufacture and assemble, due to a reduction in the number ofparts and the overall simple and streamlined design. This can compensatefor the fact that there is no opportunity to repair or maintain thevalve assembly for the duration of the flight.

The valve assembly can include a motor mount, mounting stanchions, valvehead, a driveshaft, a bearing assembly, a motor coupler, and a motor.The motor mount may be the base structure to which the variouscomponents of the valve assembly are mounted. The mounting stanchionscan be used to join the valve assembly to the compressor inlet.

The valve head can be configured to increase or decrease thecircumferential area of the inlet opening through which air can travelto or from the compressor inlet and the envelope.

The movement of the driveshaft controls movement of the valve head intoand away from the compressor inlet. The bearing assembly can extendaround the driveshaft to facilitate rotational movement of thedriveshaft. The motor coupler and the motor further facilitates rotationof the driveshaft, which further causes movement of the valve along thedriveshaft between a fully extended distal position and a retractedproximal position.

In a fully extended position, the valve head and a seal carried by thevalve head can be pressed up and into the air compressor inlet. Thevalve head can hold the gas or fluid contents of an envelope (outer orinner envelope) of the unmanned aerial vehicle. As the valve head movesinto a retracted position away from the inlet and into the retractedproximal position, the seal retracts from the surface of the compressorinlet, allowing the fluid contents of the envelope to escape to theexternal environment of the unmanned aerial vehicle.

Thus, the features of the valve assembly disclosed herein provide for aconfiguration that allows for an effective structure to control the sizeof the circumferential opening of the inlet to which the valve assemblyis attached, and ultimately to determine how much air is allowed intoand out of the envelope. The features of the disclosed valve assemblycan allow for effective operation of the valve assembly at highaltitudes and allows for the contents of the envelope to remain sealedwithin the envelope at extremely low air temperatures, or for theenvelope to be unsealed for either the addition or removal of ballastgas (e.g., air).

4. Overview: Electronics Control Assembly for Altitude Control System

Terrestrial applications for devices that must operate in explosiveenvironments typically prevent catastrophe by being designed in an“intrinsically safe” way such that the system never has enough energystored within it to exceed the energy of activation of the gasenvironment. Terrestrial intrinsic safety requirements require thatthere be less than 15 Joules in the circuit of the altitude controlsystem at any given time. However, the components of the altitudecontrol system: air compressor assembly, valve assembly, electronicscontrol assembly, all require energy close to and/or in excess of 15,000Joules. If a failure in any one component of the system causes a sparkand an explosive gas is present, explosion may occur. Knownprecautionary measures that address these problems, however, tend to beextremely heavy and incompatible for use with unmanned aerial vehiclessuch as stratospheric balloons.

To address these issues and improve safety for altitude control systemsutilized in unmanned aerial vehicles employing explosive gases, aspecialized electronics control assembly may be used. The electronicscontrol assembly may be mounted at the top of the compressor of thealtitude control system, but it can also be located in other locationswithin sufficient distance to allow for communication with the altitudecontrol system. The electronics control assembly can include manycomponents, such as a motor thermal sensor, an electronic speed controlthermal sensor, a compressor housing thermal sensor, a barometer, and adifferential pressure sensor.

The altitude or direction of the unmanned aerial vehicle may bedetermined and controlled by an electronic control system, whichincludes a computing device that can cause the unmanned aerial vehicleto adjust its altitude to an altitude corresponding with a predeterminedheading. In embodiments, the computing device may send a signal or datapacket to a controller, the data packet including the altitudecorresponding with the selected heading. In response, the controller maycause the unmanned aerial vehicle to adjust its altitude based on thepredetermined flight path.

Thus, the electronic control system according to aspects of thedisclosure can monitor current weather conditions, temperatures, andconditions within unmanned vehicles to better control and coordinate theoperation of the air compressor assembly and valve assembly. This allowsfor an efficient altitude control system that can readily adjust thealtitude and heading of the unmanned aerial vehicle.

5. Overview: Improved Safety Features for the Altitude Control System

When the altitude control system is used in connection with an unmannedaerial vehicle employing the use of explosive gases, such as explosivelift gas in a stratospheric balloon, there is a need to implement safetyfeatures within the altitude control system. Such safety features can beimplemented within one or more assemblies within the altitude controlsystem and can include early detection of gas leaks that can lead toignition of the explosive gas, as well as enhanced structural featuresthat better withstand and avoid the ignition of flammable gas.

5a. Improved Safety Features for the Compressor

A compressor motor, typically requiring hundreds of watts to operate,requires too much power to be made intrinsically safe. Secondary andtertiary safety provisions must be utilized to accommodate potentialcompressor motor failure. Thus, the materials and structure of an aircompressor can be modified to increase the ability of the compressor towithstand an explosion that can occur when the air compressor is usedadjacent explosive gases, such as use of the compressor adjacent aballoon envelope filled with explosive gases.

To prevent the electrical energy in the motor stator from shorting toground or to another motor phase, slot liners for the various motorphase slots can be implemented and then double varnished or otherwiseimproved in dielectric strength. Compared to a traditionalsingle-varnished motor, this adds two additional dielectric barriers forsecondary and tertiary fault tolerance and increases the overalldielectric strength of the system. The compressor can also be formedfrom non-sparking materials such as brass or stainless steel.

Thus, these improved compressor safety features help to better regulatemotor failure, as well as the possibility of sparking, which can causecombustion of the gases within the balloon.

5b. Improved Safety Features for the Valve Assembly

A toughened housing around the energy-carrying elements such as thedrive motor and associated electronics can be designed to specificallywithstand explosion in the valve assembly. For example, the valve motormay be enclosed in an explosion proof housing having a reinforcedstructure such that if a failure in the motor causes a spark in thepresence of explosive lift gas, the resulting explosion is containedwithin the explosion proof housing. Several additional features may alsobe included in the valve housing design. Explosion proof seals on everypenetration of the valve housing can be utilized. For example, the cablepass through can be strengthened and a shaft seal can be provided on thedriveshaft of the valve mechanism. A small vent may be left with aflame-arresting feature which allows the system to “breathe,” butprevents a flame from exiting and causing an external ignition byquenching or arresting the flame before the flame is able to exit thehousing. Thus, these improved valve assembly safety features help toensure that possible valve motor failure or other failure of the valvewill not result in the ignition of explosive gases used within thesystem.

5c. Improved Safety Features for Control Electronics

The control electronics, like the compressor motor, may require moreenergy than “intrinsically safe” guidelines allow when using withexplosive gasses. As such, the control electronics can also be designedto be operationally safe. For instance, thermal/environmental housingaround the electronics can seal them off from the local air environment,preventing the explosive gas from direct exposure to energized tracesand components on the board. In addition, current sensors on the boardcan also be used to track the current going into and out of the threephases of the compressor and valve motors. Thus, the extra safeguardsfor the control electronics provide for another means for providing asafer altitude control system by attempting to seal the motor from beingexposed to explosive gas. Additionally, sensors that can be used topredict possible future failure can allow for a user of the system toshut down the system before the explosive gases can be caused to ignite.

A. Examples of a System, Balloon of the Example System, and ExampleAssemblies and Example Safety Features of an Example Altitude ControlSystem of the Example System

1. Example System

FIG. 1 depicts an example system 100 in which an unmanned aerial vehicleas described above may be used. This example should not be considered aslimiting the scope of the disclosure or usefulness of the features ofthe present disclosure. For example, the techniques described herein canbe employed on various types of unmanned aerial vehicles and systems. Inthis example, system 100 may be considered a “balloon network” though inaddition to balloons the network may include other types of unmannedaerial vehicles including other airships, etc. As such, the system 100includes a plurality of devices, such as balloons 102A-F, ground basestations 106 and 112 and links 104, 108, 110 and 114 that are used tofacilitate intra-balloon communications as well as communicationsbetween the base stations and the balloons. One example of a balloon isdiscussed in greater detail below with reference to FIG. 2.

2. Example Aerial Vehicle

FIG. 2 is an example aerial vehicle, here a balloon 200, which mayrepresent any of the balloons of the system 100. As shown, the balloon200 includes an outer envelope 210, a payload 220 and a plurality oftendons 230, 240 and 250 attached to the outer envelope 210. The balloonouter envelope 210 may take various forms. In one instance, the balloonouter envelope 210 may be constructed from materials such aspolyethylene that do not hold much load while the balloon 200 isfloating in the air during flight. Additionally, or alternatively, someor all of outer envelope 210 may be constructed from a highly flexiblelatex material or rubber material such as chloroprene. Other materialsor combinations thereof may also be employed. Further, the shape andsize of the outer envelope 210 may vary depending upon the particularimplementation. Additionally, the outer envelope 210 may be filled withvarious gases or mixtures thereof, such as helium, hydrogen or any otherlighter-than-air gas. The outer envelope 210 is thus arranged to have anassociated upward buoyancy force during deployment of the payload 220.

The payload 220 of balloon 200 may be affixed to the envelope by aconnection 260 such as a cable or other rigid structure. The payload 220may include a computer system (not shown), having one or more processorsand on-board data storage. The payload 220 may also include variousother types of equipment and systems (not shown) to provide a number ofdifferent functions. For example, the payload 220 may include variouscommunication systems such as optical and/or RF, a navigation system, apositioning system, a lighting system) a plurality of solar panels 270for generating power, a power supply (such as one or more batteries) tostore and supply power to various components of balloon 200.

In view of the goal of making the balloon outer envelope 210 aslightweight as possible, the balloon envelope may be comprised of aplurality of envelope lobes or gores that have a thin film, such aspolyethylene or polyethylene terephthalate, which is lightweight, yethas suitable strength properties for use as a balloon envelope. In thisexample, balloon outer envelope 210 is comprised of envelope gores210A-210D.

Pressurized lift gas within the balloon outer envelope 210 may cause aforce or load to be applied to the balloon 200. In that regard, thetendons 230, 240, 250 provide strength to the balloon 200 to carry theload created by the pressurized gas within the balloon outer envelope210. In some examples, a cage of tendons (not shown) may be createdusing multiple tendons that are attached vertically and horizontally.Each tendon may be formed as a fiber load tape that is adhered to arespective envelope gore. Alternately, a tubular sleeve may be adheredto the respective envelopes with the tendon positioned within thetubular sleeve.

Top ends of the tendons 230, 240 and 250 may be coupled together usingan apparatus, such as top plate 201 positioned at the apex of balloonouter envelope 210. A corresponding apparatus, e.g., bottom plate 214,may be disposed at a base or bottom of the balloon outer envelope 210.The top plate 201 at the apex may be the same size and shape as andbottom plate 214 at the bottom. Both caps include correspondingcomponents for attaching the tendons 230, 240 and 250 to the balloonouter envelope 210.

FIG. 3 is an example of balloon 200 in flight. In this example, theshapes and sizes of the outer envelope 210, connection 260, innerenvelope 310, and payload 220 are exaggerated for clarity and ease ofunderstanding. During flight, these balloons may use changes in altitudeto achieve navigational direction changes. In this regard, the innerenvelope 310 may be a ballonet that holds ballast gas (e.g., air)therein, and the outer envelope 210 may hold lift gas around theballonet. Alternatively, in a reverse ballonet configuration, the innerenvelope 310 may hold lift gas therein and the outer envelope 210 mayhold ballast gas (e.g., air) around the inner envelope 310, and theinner envelope 310 may hold the lift gas therein.

An altitude control system 320 may be positioned at the bottom plate 214of the balloon to effect changes in altitude. FIG. 4 is an exploded viewof an example altitude control system that includes a (1) mixed flowcompressor assembly 400 with inlet-mounted motor; (2) valve assembly500; and (3) electronics control assembly 600. The compressor assembly400 can include a ballonet shroud 401 that can be directly joined to andpositioned within an opening in the bottom plate 214. The valve assembly500 can be directly connected to an opening in the air compressor toregulate the amount of air into and the contents out of the compressor.The electronics control assembly 600 can be positioned within an openingto the ballonet shroud 401.

The compressor assembly 400 of the altitude control system can causeballast gas (e.g. air) to be pumped into the inner envelope 310 withinthe envelope 210, which increases the mass of the balloon and causes theballoon to descend. Similarly, a valve head 502 (see FIG. 11) of thevalve assembly 500 may retract from the inlet of the air compressor andmay cause air to be released from the inner envelope 310 (and expelledfrom the balloon) in order to reduce the mass of the balloon and causethe balloon to ascend. The electronics control assembly 600 may bemounted at the top of the compressor assembly 400.

3. Example Air Compressor with Inlet Mounted Motor

FIG. 5 is an example compressor assembly 400 for use with the altitudecontrol system 320. The compressor assembly 400 can be used to changethe amount of air within an envelope (such as an outer envelope 210and/or the inner envelope 310) by allowing for an increase or decreasein the amount of air provided to the envelope. For instance, acompressor of the air compressor assembly can be configured to provideair to the envelope at a rate and volume of air to allow for flight athigh altitudes. For example, when a change in altitude is desired, thecompressor can drive air into the envelope 210 and/or the inner envelope310, thereby increasing the overall density of the system. This willcause the balloon to descend and decrease in altitude.

In one example, as shown in the cross-sectional view of FIG. 6 (throughA-A of FIG. 5), the compressor assembly 400 can be a mixed flowcompressor that includes a compressor inlet 402, an outlet 404, and acompressor motor 406 mounted at the compressor inlet 402 of thecompressor assembly 400. This mixed flow compressor design can allow forthe use of a small and high power density motor to power the aircompressor by counteracting high levels of heat generated by the motorand causing motor failure. Furthermore, because unmanned aerial vehiclessuch as stratospheric balloons and airships primarily rely upon windcurrents for movement, there is no need for an air compressor to producehigh pressure or high velocity to move the balloon at high speeds. Mixedflow compressor designs in the configuration disclosed herein thereforeprovide a suitable solution for inclusion of an efficient air compressorassembly within an unmanned aerial vehicle.

The mixed compressor assembly 400 may include various structuralfeatures. For example, as shown in FIG. 6, the mixed flow compressor caninclude a diffuser 408, a compressor housing 410, including a primarycompressor housing 410 a and a secondary compressor housing 410 b, acompressor motor 406 mounted within the compressor inlet 402 and animpeller 412. When assembled together, these components define a cavity414 or plenum of the mixed compressor assembly 400. As shown, the cavity414 may be a central cavity.

The compressor housing 410 can be generally cylindrical. An entrance oropening 416 at the entrance to the compressor inlet 402 of thecompressor assembly 400 can form an intake for air. The compressorhousing 410 defines a cavity 414 therethrough to enable air or otherfluid to flow into and out of the compressor housing 410. In oneexample, the cavity 414 extends entirely through the compressor housing,with the interior surface 409 of the compressor housing forming aperimeter of the cavity 414. The opening 416 can have an inlet openingdiameter ID1 that is greater than the diameter D1 of the majority of alength of the cavity 414. This can allow for greater intake of air atthe entrance to the compressor inlet 402.

The overall shape of the compressor housing 410 can define a generallydish-shaped profile having a circular configuration. For example, anouter dimension of the compressor housing 410 may decrease along alongitudinal axis X-X defined through a center portion of the compressorhousing 410. Although generally illustrated as having a circularconfiguration that corresponds to the circular configuration of thediffuser 408, the compressor housing 410 may alternatively include anysuitable configuration, and may be the same or different configurationas the diffuser 408. The compressor housing 410 may be formed of atleast one of aluminum, brass, or stainless steel, although other typesof material may be contemplated.

The compressor housing 410 can include a primary compressor housing410(a) and a secondary compressor housing 410 b joined together to formthe completed compressor housing 410. Alternatively, a monolithichousing may be used, or a compressor assembly comprised of more than twoprimary portions may be used. As shown in FIG. 6, the primary compressorhousing 410 a extends between a first surface 422 and an opposing secondsurface 424. The second surface 424 of the primary compressor housing410 a transitions to a lower inlet portion 402 a having a cylindricalprofile that is coaxial with the longitudinal axis X-X. In this manner,the profile of the compressor housing 410 transitions from a cup or dishshaped profile to a cylindrical profile. The primary compressor housingextends from the second surface 424 to a third surface 426 at theopening to the compressor inlet 402. The shape of the primary compressorhousing 410 a can allow for an upper compressor portion 411 a, which hasa diameter D2 that is greater than a diameter D1 of a lower compressorportion 411 b.

The secondary compressor housing 410 b can be positioned between theprimary compressor housing 410 a and the diffuser 408. The secondarycompressor housing may have a generally cylindrical profile. An interiorcavity 420 may extend therethrough and form an upper inlet portion 402 bof the compressor inlet 402. The secondary compressor housing 410 b canbe sized to fit within the upper compressor portion 411 a of the primarycompressor housing 410 a. A flange 428 of the secondary compressorhousing 410 b can be attached to the second surface 424 of the firstprimary compressor housing to secure the secondary compressor housing410 b within the primary compressor housing. Once the primary andsecondary compressor housings 410 a and 410 b are joined together, thecavity 414 of the primary compressor housing 410 a and the interiorcavity 420 of the secondary compressor housing 410 b are aligned alongthe X-X axis to form the cavity 414 or plenum extending through thelength of the compressor assembly 400. The diffuser 408, primarycompressor housing 410 a, and compressor motor 406 are attached to thesecondary compressor housing 410 b.

The diffuser 408 includes a first curved lower portion 408 a that can beattached to the secondary compressor housing and a curved upper portion408 b spaced apart from the first curved lower portion 408 a so as todefine a conduit or passageway 438 therebetween. This passageway 438 mayallow air moving through the cavity 414 to freely flow out of thesecondary compressor housing 410 b and the compressor assembly 400 andfor instance, into an envelope an envelope (such as outer envelope 210and/or the inner envelope 310). As shown, the diffuser 408 may have agenerally planar configuration with a circular profile. Of course, thediffuser may include any suitable profile, such as square, rectangular,and oval, amongst others.

The diffuser 408 may be configured to convert the mechanical work doneby the compressor motor 406 and impeller 412 of the compressor assembly400 back into potential energy in the form of pressurized air. Becauseof the shape of the diffuser 408, the diffuser changes the direction ofthe compressed air and slows and expands the air. As such, the diffusercan efficiently convert the kinetic energy of the compressed, flowingair into higher pressure, static air in the outer envelope 210 and/orinner envelope 310 of the balloon.

A motor housing 407 may house a compressor motor 406. The compressormotor 406 may be of any variety with sufficient torque and speed todrive the system. For instance, the motor may be a brushless DC, brushedDC, or another suitable motor so long as the motor is paired with asuitable controller to operate the motor.

The compressor motor 406 and its motor housing 407 can be positionedwithin the compressor inlet 402 of the compressor assembly 400. Forexample, the motor housing 407 may be positioned along and aligned withthe axis x-x extending that extends through the cavity 414 andcompressor inlet 402 of the compressor assembly 400. The impeller 412can overlie the compressor inlet 402, compressor motor 406, and motorhousing 407. In this configuration, the compressor inlet 402 can extendan entire length of the cavity 414 of the compressor housing 410 up tothe impeller 412, such that the entire motor housing 407 can bepositioned within the compressor inlet 402. The motor housing 407 cantherefore be positioned between the opening 416 to the compressor inlet402 and the impeller 412. The impeller 412 can be positioned at theoutlet 404 of the compressor housing 410.

The inlet end 407 b of the motor housing 407 can be positioned closer tothe opening 416 of the compressor inlet 402 than the impeller 412. Inthe example shown, the motor housing can be positioned so that the outersurface 442 of the motor housing 407 is spaced away from the interiorsurface 409 of the compressor housing 410. This can allow for the freeflow of air all around the outer surface 442 of the motor housing 407.

The motor housing 407 can be shaped to allow for substantial portions ofthe motor housing 407 to be positioned within the cavity 414. An examplemotor housing 407 is shown in FIG. 7 (and the correspondingcross-sectional views in FIGS. 8 and 9). In this regard, FIG. 7 providesa view of the motor housing 407 removed from the compressor housing 410for ease of discussion. The motor housing 407 may be partiallypill-shaped, with a main body 407 a having an elongated length L greaterthan its W, and the inlet end 407 b that is curved. The motor housing407 can take on any other shapes sized to fit within the cavity 414 andcompressor inlet 402, including, square, rectangular, curved.

The motor housing 407 may be coupled to the compressor housing. Forexample, the motor housing 407 may be press fit, thermally press fit,attached by fasteners, brazing, welding, or other suitable means to thecompressor housing. In the example shown, mounting fins 440 extendingfrom the motor housing 407 may be used to attach the motor housing 407to the secondary compressor housing 410 b. As shown, the mounting fins440 may be elongated and extend along a majority of the length of themotor housing 407, but may also extend along more or less of the motorhousing 407. The mounting fins 440 may be tear-drop shaped to allow forair to flow around and over the mounting fins 440, though other shapesmay also be used. In this example, the widest part W of the mounting fin440 is positioned closer to the inlet end 407 b of the motor housing andmay be tear-drop shaped. The tip 439 of the mounting fin 440 ispositioned closer toward atop 441 of the motor housing 407 than theinlet end 407 b.

The mounting fins 440 can extend around the circumference of the motorhousing 407. For example, two or more fins can be provided to mount themotor housing 407 to the compressor housing. Three or more fins canprovide for greater stability and to aid the extraction of heat from thecompressor assembly 400. In one example, as shown in FIG. 8, across-sectional view through B-B of FIG. 7, three mounting fins extendaround the motor housing. The mounting fins 440 may be equally spaced120° apart from one another. The arrangement of the mounting fins cancreate passageways P within the central cavity to direct air through thecavity of the housing. Additionally, the mounting fins 440 can becomprised of a thermally-conductive material that can draw heat from themotor. In one example, the mounting fins can be comprised of copper, butother thermally-conductive materials can be used.

When the unmanned aerial vehicle, such as balloon 200, is in flight, thecompressor motor 406 can cause rotation of the driveshaft 444, which inturn causes the impeller 412 to rotate. As the compressor motor 406continues to rotate the driveshaft 444 and impeller 412, excessiveamounts of heat are generated by electrical losses in the motor elementsand mechanical losses in the bearings. Generating excess amounts ofwaste heat results in the loss of air that could have been becompressed, thereby resulting in an inefficient compressor.

To dissipate heat generated by the driveshaft rotation, the motorhousing can be cooled down. In one example, air can be drawn from theenvironment surrounding the altitude control system 320 into the opening416 of the compressor inlet 402 of the compressor housing 410. The airdrawn from the environment at high altitudes is extremely cold, and canbe at least as low as, for example, 55° C. The air drawn from theenvironment may pass through the lower portion of the compressor inlet402 and around the motor housing 407. The air can then be distributedinto passageways P created by the mounting fins 440 positioned withinthe cavity 414. As the air passes over the mounting fins 440, the air isforced to accelerate over the widest part W of each of the mounting fins440. This distribution of the air through the passageways P and aroundthe motor housing 407 may cool down the motor and dissipate heat. At thesame time, this may help to prevent excess heat generated by the motorfrom damaging the various parts of the motor. Air can be acceleratedthrough the passageway and then compressed, as the air passes through bythe impellers. The air is then caused to slow down by the diffuser, asthe air exits the cavity 414 and is diffused through the diffuser 408.

Positioning the compressor motor 406 and motor housing 407 as shown inFIG. 6, for instance within the compressor inlet 402 and, according tothe path of air flow from the compressor inlet 402 to the outlet 404,prior to the impeller 412 and outlet 404, may enable the use of a motorthat has high power density. This is because heat generated by such highpower density motor is transferred to the flowing cold air.

The mixed compressor assembly 400 combines axial and radial componentsto produce a diagonal airflow compressor stage or compressed air thatexits the air compressor assembly at an angle to the axis. For example,in the present design, the exit mean radius of the airflow can begreater than at the inlet, like in a centrifugal design, but the flowwill exit the compressor in a direction tangential to the axial airflow.The airflow will enter the compressor through the inlet and pass throughthe compressor in an axial direction, but due to the angled edge of thecompressor housing and diffuser, air is routed tangentially away fromthe axial direction. For example, the air may be dispersed through theoutlet at a 45 degree angle, but the angle may range from 25 to 65degrees. In other examples, the angles may alternatively be below 25degrees and greater than 65 degrees.

The features of the disclosed mixed flow compressor assembly with themotor positioned at the inlet can allow for a compressor assembly thatis significantly more efficient than prior versions. For example, FIG. 9illustrates a chart that compares the efficiency of: (1) the present airflow compressor assembly (bottom line of the chart)—one where the motorhousing is positioned within the inlet of the compressor housing betweenthe impeller and the intake; and (2) prior compressor assembly that doesnot include a motor positioned within the inlet (top line of chart). Theprior compressor assembly may be a centrifugal compressor that is twiceas heavy and includes an outlet-mounted motor (i.e., the motor ismounted above the diffuser instead of below the impeller). As shown, theefficiency of the present compressor design-mixed flow processor withinlet mounted motor is significantly greater than the efficiency of theprior compressor design. The present design is capable of achieving thesame

Other types of air compressors may be used in place of the mixedcompressor assembly 400, in combination with the other subassemblies ofthe altitude control system 320 (i.e., the valve assembly, controlelectronics control assembly, and features of the mixed flow aircompressor assembly, such as preloading) discussed herein. Some of thesealternative air compressors may be more or less efficient, lesseffectively address the heat issues, and/or require reconfigurationand/or reorientation of one or more components of the compressors.Nonetheless, the use of such compressors can alternatively be used toadjust the altitude and direction of an unmanned aerial vehicle.

4. Example Dynamic Axial Preloading Assembly for Air Compressor BearingAssembly

The example compressor assembly 400 can further include a preloadingassembly 446 for a rotating shaft assembly of the compressor assembly ofan unmanned aerial vehicle, such as balloon 200. The preloading assembly446 may be a dynamic preloading assembly and may address theshortcomings associated with failure of the rotating shaft assembly dueto external forces that can cause the bearing assembly to fail. Forexample, back pressure from within the envelope an envelope (such as theinner envelope 310 or the outer envelope 210 in the case of a reverseballonet configuration), mismatched coefficient of thermal expansionbetween the steel driveshaft and aluminum housing, and large temperaturechanges caused by the environment surrounding a device within theunmanned aerial vehicle.

FIG. 10 illustrates an enlarged cross-sectional view of the motorhousing 407 though C-C of FIG. 7 of the compressor assembly 400depicting preloading assembly 446. For ease of discussion, FIG. 10includes only the components necessary to describe the preloadingassembly 446, and features such as the impeller 412 are not included inFIG. 10. As shown, the compressor motor 406 is housed within the motorhousing 407. The rotating shaft assembly can include the rotatingdriveshaft 444 coupled at one end to the impeller 412, a first bearingassembly 452 that is positioned within a bearing housing or carrier 460,and a second bearing assembly 454 that is positioned at an opposed endadjacent the impeller 412. The preloading assembly 446 includes abearing carrier 460 and a biasing element, such as a spring 462, toexert a force on the bearing carrier 460, so as to “float” or springload the bearing assembly that supports the shaft assembly.

The first and second bearing assemblies can facilitate rotation of therotating shaft assembly. The first bearing assembly 452 can be a ballbearing assembly. A first inner race 456 a can be attached to and extendaround the circumference of the driveshaft 444. A second outer race 458a can be radially spaced apart from the first inner race 456 a by ballbearings 459 and can extend around the circumference of the driveshaft444. The second outer race 458 b can be coupled to the bearing carrier460 and in this example can be fixed to the bearing carrier 460. Thefirst inner race 456 a can rotate with the driveshaft 444 relative tothe fixed second race 458 a.

The second bearing assembly can also be a ball bearing assembly, with afirst inner race 456 b, a second outer race 458 b, and ball bearings 459b disposed between the first and second races 456 b, 458 b. The secondouter race 458 b can be coupled to the bearing carrier 460 and in thisexample can be fixed to the bearing carrier 460. The first inner race456 a can rotate with the driveshaft 444 relative to the second race 458a which may be fixed.

The bearing carrier 460 can be directly coupled to the first bearingassembly 452 and can be configured to move in an axial direction alongthe axis X-X of the driveshaft 444. The bearing carrier 460 may be acylindrical bore having a first upper portion 464, a second lowerportion 466, and an intermediate projection 468 separating the first andsecond portions 464, 466. The intermediate projection 468 includes a topsurface 470 and an opposed bottom surface 472. The top surface 470 canprovide a seating surface that supports at least a portion of the firstbearing assembly 452. For example, the first bearing assembly 452 may bepositioned within the bearing carrier and such that the top surface 470supports the second outer race 458 b of the first bearing assembly 452.As shown, the top surface of the intermediate projection can be indirect contact with the second outer race 458 b of the first bearingassembly 452.

To keep the bearing carrier 460 from rotating with the supporteddriveshaft assembly, an anti-rotation device may be used. For example, amachine key 461 arranged within in a slot, a series of guide pins, orany other device with axial clearance can be used to limit rotationalmovement of the bearing carrier 460 within the motor housing 407.

A biasing element may be coupled to the bearing carrier 460. The biasingelement may be any element configured to exert a force on the bearingcarrier 460. As shown in the example of FIG. 10, the biasing element maybe a spring 462 positioned in the second portion 466 of the bearingcarrier 460 and in contact with the bottom surface 472 of theintermediate projection 468. For example, the spring may be atraditional helical spring or a wave spring. Such spring may be madefrom steel or aluminum, but other materials may also be used.Alternatively, the biasing element may be a plurality of conical springwashers, such as Belleville washers. Other types of biasing elements maybe contemplated.

The biasing element may be positioned with the second lower portion 466of the bearing carrier 460. For instance, the spring 462 may fit withinand occupy the second lower portion 466 of the bearing carrier. The topsurface 463 of the spring 462 can be positioned directly adjacent thebottom surface of the intermediate projection. In other examples, due tothe configuration of the spring or device, an intermediate surface canbe positioned between the spring 462 and the bottom surface of theintermediate projection 468.

The biasing element can exert a biasing force against the bearingcarrier 460 to cause movement of the bearing carrier along the axis X-Xof the driveshaft 444. For example, the spring 462 may apply a biasingforce F against the bottom surface 472 of the intermediate projection468. The biasing force F can cause movement of the bearing carrier 460in axial direction A or an axial direction B, as shown in FIG. 10.

The biasing force can provide an axial preload of the first bearingassembly 452. For example, because the bearing carrier 460 supports thesecond race 458, movement of the bearing carrier causes movement of thesecond race 458 a relative to the first inner race 456 a due to thebiasing force. The second bearing assembly 454 can also be axiallypreloaded by the movement of the bearing carrier 460 and the preloadingforce.

As noted above, when the unmanned aerial vehicle, such as balloon 200,is in flight, the vehicle will be subject to extreme environmentalchanges. The temperature changes will then cause the components of thealtitude control assembly to expand and contract at different rates dueto the differences in thermal expansion between the shaft and componentsof the assembly formed from a different material. For example, thedriveshaft 444 may be made of steel which will have a differentcoefficient of thermal expansion than other components formed fromlighter materials, such as aluminum. Additionally, back pressure fromthe envelope (such as outer envelope 210 and/or the inner envelope 310)will also change due to the change in temperature and exert a varyingaerodynamic force/load on the impeller. Thus, the necessary preloadingforce must continually change throughout the flight of the vehicle toaccommodate these and any other forces that may cause the first andsecond races to become separated, thereby causing bearing failure.

The preloading assembly 446 may be configured to dynamically adjust thenecessary bearing preload to compensate for changing loads due todiffering rates of thermal expansion, back pressure from the envelope,and any external forces that may cause bearing failure. For example,back pressure from the envelope and/or the forces on the driveshaft 444caused by differing rates of thermal expansion may decrease or increaseover time. The spring can apply a force F to the bearing carrier that isequal to the initial backpressure force, but as the backpressure forcedecreases, the spring may accommodate for the decrease and also decreasethe force applied to the bearing carrier. This decrease in force maycause the bearing carrier 460 to move in a downward direction B, therebyalso causing the second races 458 a, 458 b of the first and secondbearing assemblies 452,454 to move in a downward direction. Similarly,if the backpressure increases, the spring may apply an increased force Fin response to the increased back pressure force causing an upward axialforce and the bearing carrier 460 to move in an upward direction. Thespring can increase or decrease the force applied to the bearing carrier460 based on the forces created by the extreme temperature changes andthe resulting expansion and contraction of the components that havediffering coefficients of thermal expansion. As such, the preloadingassembly 446 can essentially “float” the bearing assembly to ensure thatthe bearings are always preloaded and engaged.

Thus, the features disclosed herein, provide for an altitude controlsystem that utilizes an air compressor assembly with dynamic axialpreloading for use with an unmanned aerial aircraft. Such featuresaddress the shortcomings associated with failure of the rotating shaftassembly of a motor within the unmanned aerial vehicle due to externalforces to the bearing assembly caused by, for example, back pressurefrom within the envelope (such as outer envelope 210 and/or the innerenvelope 310), mismatched coefficient of thermal expansion between thesteel driveshaft and aluminum housing, and large temperature changescaused by the environment surrounding a device within the unmannedaerial vehicle. This can help to prevent the catastrophic failure thatwould result from unloading the bearing at high speed. The featurestherefore compensate for changes in atmosphere, backpressure,temperature, etc. that would otherwise cause bearing assembly failure.In this regard, the features disclosed eliminate the need to manufactureindividual components that separately address these shortcomings.

5. Example Valve

Returning to FIG. 4, the valve assembly 500 can be used to regulate theamount of air flowing into and out of an envelope (such as outerenvelope 210 and/or the inner envelope 310) at any given time duringflight. The valve assembly 500 can regulate, direct or control the flowof air by opening, closing, or partially obstructing variouspassageways. For example, the valve assembly 500 can be mounted to thecompressor inlet 402 of an air compressor, such as the compressorassembly 400 described above. The bell-mouth-shaped opening 416 of thecompressor inlet 402 can provide a structural connection of the valveassembly 500 to the broader altitude control system 320 and unmannedaerial vehicle. Instead of attachment to the compressor assembly 400 andthe remainder of the altitude control system 320, the valve assembly 500can also stand alone and may instead be attached to the bottom plate214, the top plate 201, directly to the envelope, or some other part ofan unmanned aerial vehicle, such as balloon 200, in order to allow fordirect access into and out of the envelope. The features of thedisclosed valve assembly 500 can allow for effective operation of thevalve assembly at high altitudes and allows for the contents of theenvelope to remain sealed within the envelope at extremely low airtemperatures.

FIG. 11 illustrates a perspective view of the valve assembly 500. Thevalve assembly 500 can include several structural components, includinga valve head 502, a driveshaft 504, mounting stanchions 506, motor mount508, and a lower valve housing 510. The valve assembly 500 can becoupled to the inlet 503 of various types of assemblies including, forinstance, the compressor assembly 400. The valve assembly can includeseveral structural components, including a motor housing 518, driveshaftassembly 512 and motor coupler assembly 514.

FIG. 12 is a cross-sectional view of the valve assembly, taken alongline D-D of FIG. 11, but shown positioned within the inlet 503 of adevice. The inlet 503 may be the same as the compressor inlet 402 of thecompressor assembly 400, but in other examples, the inlet may be theinlet of a different compressor assembly, such as a centrifugal, anaxial, or a different type mixed flow processor. The inlet 503 canalternatively be a direct inlet to the balloon envelope (envelope 210 orthe inner envelope 310) or another assembly altogether within or outsideof ballooning technology. When used in connection with stratosphericballoons, the valve assembly 500 can be directly attached to the topplate, the bottom plate, or the balloon envelope.

The motor mount 508 can be the base housing structure to which thevarious components of the valve assembly 500 are mounted. The driveshaftassembly 512 and the driveshaft 504 to which the valve head 502 ismounted, as well as mounting stanchions 506 can be attached to aninterior top surface of the motor mount 508. An exterior surface 509 ofthe motor housing 518, which is used to house the valve motor 516, canbe attached to an outer lower surface of the motor mount 508.

Mounting stanchions 506 can be used to join the valve assembly to thecompressor inlet 402. In one example, three evenly-spaced mountingstanchions 506 may extend around the perimeter of the motor mount 508.In other examples, less than three or more than three mountingstanchions may be utilized to join the valve assembly 500 to thecompressor inlet 402. A first set of mounting screws 520 a can be usedto attach a first end 522 of each of the mounting stanchions 506 to themotor mount 508. A second end 524 of the mounting stanchions 506 can bejoined by a second set of mounting screws 520 b to the compressor inlet402. Other fastening methods may also be used, including welding, heatstaking, and adhesive bonding. A trailing edge 526 of each of themounting stanchions 506 may be configured to function as a guide railfor the valve head 502.

The valve head 502 can be joined to an end of the driveshaft 504. In oneexample, the valve head 502 may be a conical-shaped device that includesa rounded bell-shaped base 532 that terminates in a tip 534. The valvehead 502 may be sized so that at least portions of the valve head 502fit within the compressor inlet 402. The conical shape of the valve head502 further acts as a guide to redirect the contents of the envelope(such as outer envelope 210 and/or the inner envelope 310) away from therest of the valve assembly 500 as the contents exits the envelope.Recesses within the valve head 502 may be configured to receive andcooperate with the edges 526 of the mounting stanchions 506 so as totravel in a vertical direction along the mounting stanchions 506, and toprevent rotation of the valve head 502 about the driveshaft 504.

The valve head 502 can be configured to increase or decrease thecircumferential area of the compressor inlet 402 through which air cantravel to or from the compressor inlet 402 and the attached envelope. Asshown in FIG. 12, a cross-sectional view of FIG. 11 taken through lineD-D, when the valve head 502 is fully extended, at least a portion ofthe valve head 502 is positioned within the compressor inlet 402, so asto close off the area of the opening 416 at the compressor inlet 402.The valve head 502 can also be retracted away from the compressor inlet402 so as to increase the area of the opening 416 provided at thecompressor inlet 402 from partially open to completely open. The valvehead 502 can be moved from the fully extended position to the fullyretracted position, as well as any position therebetween. The edges 526of the mounting stanchions can guide the valve head 502 as the valvehead moves axially toward and away from the compressor inlet 402. Thevalve head 502 can throttle the flow of air, so as to increase ordecrease the amount of air into and out of the compressor inlet 402.

FIG. 13 illustrates the valve head 502 in a fully retracted positionbeneath the inlet 503. The valve head 502 is shown fully withdrawn fromthe compressor inlet 402. When fully retracted, the valve head 502 canbe positioned adjacent the top surface 511 (depicted in FIG. 12) of themotor mount 508, such that the interior surface 507 of the motor mount508 is no longer exposed and the driveshaft 504 and driveshaft assembly512 are not visible. In the retracted position, air exiting thecompressor inlet 402 will be directed away from the compressor inlet 402and around the valve head 502.

When the valve head 502 is in its fully extended position, a seal can beused to seal the compressor inlet closed so as to maintain air withinthe envelope (such as outer envelope 210 and/or the inner envelope 310).In one example, a seal 536 is positioned within a recess 501 in thevalve head 502 that extends around the outer circumference of the valvehead 502. FIG. 14 illustrates an enlarged cross-sectional view of theseal 536.

The seal 536 may be comprised of a jacket partially enclosing a biasingmechanism. For example, a jacket 538 forms a general U-shape and may besized to fit within the recess. The jacket 538 may be comprised of anyvariety of sealing materials, such as Polytetrafluoroethylene (PTFE),Polyether ether ketone (PEEK), Polyethylene, fluorosilicone and thelike. The jacket 538 may be energized by a biasing mechanism, such as aspring 540. In this regard, the seal 536 may be an energized seal.

The spring 540 can be a U-shaped spring, but any variety of springs canbe alternatively used, such as a coil spring, finger spring, or thelike. The material comprising the jacket 538 can be held in place by thespring 540, causing the jacket 538 to seal across an extremely widerange of temperatures, surface imperfections, and other conditions. Inother examples, other types of seals may be used, such as an O-ring,gasket or the like, as well as other materials used to form the seal.

A driveshaft coupled to the valve head 502 can be configured to drivethe valve head 502 into and out of the compressor inlet 402. In oneexample, the driveshaft may be a ball screw or lead screw shaft that isconfigured to translate rotary motion into linear motion. FIG. 12illustrates the driveshaft 504, along with example components of thevalve assembly that can facilitate movement of the driveshaft 504 andvalve head 502. A driveshaft housing 505 can be attached to the interiorsurface 507 of the motor mount 508 and overlie the valve motor 516. Thevalve motor may be attached to the exterior surface 509 of the motormount 508. A motor shaft 517 extends upwardly from the valve motor 516and motor housing 518 and through an opening in the motor mount 508 sothat the motor shaft 517 extends into the driveshaft housing 505 and isaligned with the driveshaft 504. The motor shaft 517 can be coupled to afirst end 542 of the driveshaft 504 by the motor coupler assembly 514.The motor coupler assembly 514 can be positioned within the driveshafthousing 505.

The driveshaft 504 can be secured within the driveshaft housing 505 andto the motor mount 508 by a series of jam nuts 546. The jam nuts maypinch the driveshaft 504 into place within the first inner race 548 ofthe driveshaft assembly 512. In one example, the jam nuts 546 can be aseries of conical spring washers on the front which act as a soft stopas well as to prevent over travel and jamming of the valve head 502 asthe valve head moves back and forth along the driveshaft.

A second end of the driveshaft 544, opposite of the first end, can beconnected to the valve head 502. The valve head 502 may be driven alongthe driveshaft 504 by a captive nut 552, which may be, for example, heatstaked, ultrasonically welded, or otherwise fastened into the center ofthe valve head 502, causing the assembly to move axially as thedriveshaft 544 rotates.

The valve motor 516 and motor housing 518 can attach to the exterior ofthe motor mount. The valve motor 516 can be held in place by a series ofsecondary motor housings, with a gas/fluid seal on the shaft of thevalve motor sealing the valve motor into a separate compartment. Thevalve motor may be of any variety with sufficient torque and speed todrive the system; the motor may be a brushless DC, brushed DC, orstepper motor so long as the valve motor is paired with a suitablecontroller to operate it.

The valve motor 516 can cause rotation of the driveshaft 504 andmovement of the valve head 502 into and away from the compressor inlet402. As the valve motor 516 rotates the driveshaft 504, the drive nutmay be rotated, and the captive nut 552, along with the valve head 502,may move along the shaft linearly.

The driveshaft assembly 512 can facilitate rotational movement of thedriveshaft 504. The driveshaft assembly 512 may overlie the driveshafthousing and be positioned around the driveshaft 504 and adjacent thebase of the driveshaft 504 to facilitate rotational movement of thedriveshaft 504. In one example, the driveshaft assembly 512 can be aball bearing assembly that includes a first inner race 548 adjacent thedriveshaft 544 and a second outer race 550 spaced away from the firstinner race 548 by ball bearings 549. The driveshaft assembly 512 can beheld in place between a jam nut 546, which threads onto the driveshaft504 and overlying the driveshaft assembly 512, and the motor couplerassembly 514.

The motor coupler assembly 514 can extend around both the motor shaft517 and first end 542 of the driveshaft 504. For example, the motorcoupler assembly 514 can couple the first end 542 of the driveshaft 504to the motor shaft 517. The motor coupler assembly 514 can be selectedthat will compensate for coefficient of thermal expansion (“CTE”)mismatches within the valve assembly 500 as well as axial misalignmentbetween the motor shaft 517 and the driveshaft 504.

The valve head 502 can be used to seal the compressor inlet. Forexample, in the fully extended position (shown in FIG. 12), the valvehead 502 and the seal can be pressed up and into the air compressorinlet. The valve head 502 can maintain the volume of gas or fluidcontents of the envelope (such as outer envelope 210 and/or the innerenvelope 310) when the compressor inlet 402 is sealed. As the valve head502 moves into the retracted position away from the compressor inlet402, the seal 536 between the compressor inlet 402 and valve head 502 isbroken, allowing the fluid contents of the envelope to escape to theexternal environment of the unmanned aerial vehicle.

The valve assembly disclosed herein may be used in connection with awide variety of applications. As noted above, the valve assembly can beused with a compressor assembly, including, for example, the mixedcompressor assembly 400, as described above. The valve assembly can besimilarly used with traditional centrifugal or axial compressorassemblies and modifications thereof. In this regard, the valve assemblymay be used in connection with a wide variety of applications, includingunmanned aerial vehicles, but may also be used in connection with anytechnology that can utilize a valve assembly.

Instead of being coupled directly to an air compressor, the valveassembly 500 may alternatively attached to the bottom or top plate andcooperate directly with the respective bottom or top plate attached tothe envelope. The valve assembly 500 can also be attached to any desiredpart of the balloon envelope, including direct attachment to the outerenvelope or the inner envelope. Similarly, the valve assembly 500 may bedirectly or indirectly attached to the balloon envelope (such as outerenvelope 210 and/or the inner envelope 310). Further, multiple valveassemblies can also be used at the same time in connection with anunmanned aerial vehicle or other systems.

Thus, the features of the valve assembly disclosed herein provide for aconfiguration that allows for an effective structure to control the sizeof the circumferential opening of the inlet to which the valve assemblyis attached, and ultimately to determine how much gas or fluid isallowed into and out of the envelope. In this regard, the features ofthe disclosed valve assembly may allow for the contents of the envelopeto remain sealed at extremely low air temperatures, such as thoseencountered in the stratosphere, or for the envelope to be unsealed foreither the addition or removal of ballast gas (e.g. air). Additionally,the valve assembly can be used to seal in gas within other systems andmay be particularly useful in low temperature conditions.

6. Example Electronics Control Assembly

The altitude or direction of an unmanned aerial vehicle, such as balloon200, may be determined and controlled by an electronics control assembly600 that can cause the unmanned aerial vehicle to adjust its altitude toan altitude corresponding with a predetermined heading. The electronicscontrol assembly for the altitude control system can be mounted at thetop of the compressor of the altitude control system. For example, anelectronics control assembly 600 can be mounted to a top of thecompressor assembly 400 of the altitude control system 320, as shown inFIG. 4.

FIG. 15 schematically illustrates example components of the electronicscontrol assembly 600. The electronics control assembly 300 can include acomputing device 606 and/or a controller 608 that can control thealtitude control system 320. As an example, the computing device and/orcontroller may include one or more processors and memory storing dataand instructions in order to enable the electronics control assembly toperform the various functions described herein.

The electronics control assembly 600 can also include various sensorsthat provide data to the computing device 606 that the computing device606 will use in making determinations regarding control of the altitudecontrol system 320. For example, the control assembly can include amotor thermal sensor 610, an electronic speed control thermal sensor612, a compressor housing thermal sensor 614, a barometer 616, adifferential pressure sensor 618, a current sensor 620, and a gas sensor622. The motor thermal sensor 610 may be configured to determine thetemperature of the motor housing 518 of the valve assembly 500, theelectronic speed control thermal sensor 612 can be configured todetermine the temperature of the electronic speed control circuitcontrolling the valve motor 516, the compressor housing thermal sensor614 can be configured to determine the temperature of the compressorhousing of the system, the barometer 616 can be configured to determinethe ambient pressure of the surrounding atmosphere, and the differentialpressure sensor 618 can be configured to compare the pressure betweenthe surrounding atmosphere and the interior of the envelope (such asouter envelope 210 and/or the inner envelope 310). The electronicassembly can further include a printed circuit board assembly havingprocessors and other circuit elements to control operation of the valvemotor 516.

In one example, the computing device 660 may send a signal or datapacket to the controller 608. The data packet may include the altitudecorresponding with a heading or wind vector selected by the computingdevice 606. In response, the controller 608 may cause the unmannedaerial vehicle to adjust its altitude based on the predetermined flightpath. For example, if the selected heading corresponds to an altitudethat is lower than the current altitude of aerial vehicle, the computingdevice 606 can cause aerial vehicle to decrease its altitude. This can,for example, involve causing the valve to retract from the compressorinlet while the compressor assembly 400 drives air into the envelope(such as outer envelope 210 and/or the inner envelope 310), therebyincreasing the overall density of the system and causing a decrease inaltitude to a lower point of neutral buoyancy.

Likewise, if a heading is selected by the computing device 60 thatcorresponds to an altitude that is higher than the current altitude ofaerial vehicle, the computing device can cause the aerial vehicle toincrease its altitude. For example, the valve head 502 of the valveassembly 500 may be opened to vent some or all of the contents (e.g. airand/or lift gas depending upon the envelope) of the envelope (which maybe either the outer envelope 210 or the inner envelope 310, therebycausing the density of the system to decrease and the unmanned aerialvehicle to rise ensure that the envelope contents remain within theenvelope.

Thus, the features of the disclosed electronic assembly allow foreffective operation of the assemblies of the altitude control system,including the compressor assembly and the valve assembly.

7. Safety Features in View of Explosive Gasses

The altitude control system may be used in connection with an unmannedaerial vehicle that relies upon the use of air alone for lift oralternatively, with a vehicle that requires the use of explosive gases,such as lift gas in a stratospheric balloon. There is a need toimplement safety features within altitude control systems that are usedwith explosive gases to both prevent and protect against the ignition ofthe explosive gases within either the outer or inner envelope. Suchsafety features can be implemented within one or more assemblies withinthe altitude control system, or within one or more assemblies that areused in connection with other types of systems where such assembly maybe useful.

7a. Improved Safety Features for the Compressor

A compressor motor may require hundreds of watts to operate. In certaincircumstances, such as those involving flammable gases, this may exceedthe amount of power for the compressor to be considered intrinsicallysafe. Secondary and tertiary safety provisions may therefore be utilizedto improve the operational safety of the device. Thus, the materials andstructure of any type of compressor assembly, including the mixed flowassembly, can be modified to increase the ability of the compressor towithstand an explosion.

To prevent the electrical energy in the motor stator from shorting toground or to another motor phase, slot liners for the various motorphase slots can be implemented and then the stator may be doublevarnished or otherwise improved in dielectric strength. The slot linerscan be custom designed and/or commercially available or modified slotliners that can provide electrical insulation. Slot liners can alsoprovide protection from electrical and mechanical stress. One example ofa commercially available slot liner is Nomex®, but other commerciallyavailable slot liners may also be implemented.

In some examples, the double varnishing can be accomplished by providingtwo layers or applications of a varnish coating on the slot liners.Compared to a traditional single-varnished motor, this (coupled with theslot liner above) adds two additional dielectric barriers for secondaryand tertiary fault tolerance and increases the overall dielectricstrength of the system. A commercially available example of a suitablevarnish is Dolphs! varnish, but other types of varnish may also beutilized. Alternatively, two layers of another dielectric coating orother dielectric fluid can be used. For example, the stator can besprayed or dipped with powder coat or epoxy. As shown in FIG. 16, across-sectional view of a portion of the motor stator 580, slot liners590 are positioned within opening 582 in the motor stator 580.

The materials selected to form the compressor can be selected fromnon-sparking materials. For example, brass or stainless steel areexemplary materials that can be used to form the compressor.Alternatively, when sparking materials are used within the compressorassembly, the sparking materials may be coated with anelectrically-conductive conversion coating to inhibit sparking. Forexample, aluminum, can be coated with an electrically-conductiveconversion coating. Examples of commercially available conversioncoating can include Alodine or SurTec 650.

Thus, these improved compressor safety features help to better regulatemotor failure, as well as the possibility of sparking, which can causecombustion of the gases within the balloon

7b. Improved Safety Features for the Valve Assembly

The valve assembly may be used in a wide variety of applications,including use within the altitude control system of an unmanned aerialvehicle. In certain circumstances, such as those involving flammablegases, the components of the valve assembly, including the drive motor,are prone to sparking that can cause the ignition of these gases.

To anticipate possible ignition of gases within the valve assembly, atoughened housing around the drive motor can be designed to specificallywithstand explosion in the valve assembly. For example, FIG. 12illustrates that the valve motor 516 may be enclosed within the lowervalve housing 510. The lower valve housing 510 may be manufactured to beexplosion proof and have a reinforced structure. Should the motor causea spark in the presence of explosive lift gas, the resulting explosioncan be contained within the lower valve housing 510.

The strength required for the lower valve housing 510 to withstand anexplosion can be calculated. Based on the free volume within the lowervalve housing 510, if the explosive stoichiometric gas mixture ispresent in the explosion proof housing, the resulting pressure may beobtained. In this manner, the explosion proof lower valve housing may beconfigured to withstand explosion with a safety factor of, e.g., 3.

Several additional features may also be included in the lower valvehousing 510 design. Explosion proof seals on every penetration of thevalve housing can be utilized. For example, the cable pass through 554can be strengthened and a shaft seal 556 can be provided on thedriveshaft of the valve mechanism. A small vent 558 may be left with aflame-arresting feature which allows the system to “breathe,” butprevents a flame from exiting and causing an external ignition byquenching or arresting the flame as before the flame is able to exit thehousing. For example, a high-aspect ratio drywall screw may be providedwithin the vent to arrest and/or quench the flame.

Thus, by containing possible failure and/or explosions to the lowervalve housing 510, as an alternative to or in addition to enhancingother features within the altitude control assembly, safety features areprovided that can protect the altitude control assembly from completefailure.

7c. Improved Safety Features for the Electronics Control Assembly

The electronics of the electronics control assembly 600, like thecompressor motor 406, may require hundreds of watts to operate. Incertain circumstances, such as those involving flammable gases, this mayexceed the amount of power for the electronic assembly to be consideredintrinsically safe. Secondary and tertiary safety provisions maytherefore be utilized so that the electronics control assembly to beoperationally safe.

A thermal/environmental housing around the circuit boards of theelectronics control assembly 600 can be used to seal off the local airenvironment. This can help to prevent the explosive gas from directexposure to energized traces and components on the circuit board. Forexample, the electronic assembly can be hermetically sealed.

Sensors configured to detect characteristics of the system that can leadto an explosion can also be implemented as a safety feature. Forexample, as shown in FIG. 16, current sensors 620 coupled to the circuitboard can also be used to track the current that goes into and out ofthe three phases of each of the compressor and valve motors. If theamount of current going into and back out of the phases does not add upcorrectly, “leakage current” is detected, which is indicative of apossible future failure. For example, dielectric materials may bedeteriorating, which can cause some of the current from a phase to“leak” to ground and potentially create a spark or short. Earlydetection of the leakage current even at extremely low levels, allowsfor the system to be shut down long before failure of the motor 516poses a safety risk.

Gas sensors can also be used to predict possible future failure. Forexample, a gas sensor 622 which monitors for the presence of explosivegases, such as hydrogen, may be used to verify that the local gascombination is or is not an explosive one. When an explosive gas isdetected, the gas sensor 622 can notify a user of the system thatexplosive gases are present and that the system should be shut downbefore the explosive gases can be caused to ignite. Alternatively, thegas sensor 622 can cause the system to be immediately shut down or shutdown within a predetermined period

Thus, the extra safeguards for the control electronics provide foranother means for providing a safer altitude control system byattempting to seal the motor from being exposed to explosive gas, aswell as providing means for early detection of events that may lead tomotor failure and/or imminent explosion.

Most of the foregoing alternative examples are not mutually exclusive,but may be implemented in various combinations to achieve uniqueadvantages. As these and other variations and combinations of thefeatures discussed above can be utilized without departing from thesubject matter defined by the claims, the foregoing description of theembodiments should be taken by way of illustration rather than by way oflimitation of the subject matter defined by the claims. As an example,the preceding operations do not have to be performed in the preciseorder described above. Rather, various steps can be handled in adifferent order or simultaneously. Steps can also be omitted unlessotherwise stated. In addition, the provision of the examples describedherein, as well as clauses phrased as “such as,” “including” and thelike, should not be interpreted as limiting the subject matter of theclaims to the specific examples; rather, the examples are intended toillustrate only one of many possible embodiments. Further, the samereference numbers in different drawings can identify the same or similarelements.

1. A system comprising: an altitude control system for an unmannedaerial vehicle comprising: a compressor assembly including: a compressorhousing including an inlet, an entrance to the inlet, an outlet, and acentral cavity extending therethrough and joining the inlet to theoutlet; a diffuser coupled to the compressor housing; a motor housingdisposed within the central cavity at the inlet of the compressorhousing; a motor disposed within the motor housing; and an impellerdisposed at an outlet of the compressor housing, the impeller coupled toa driveshaft for rotation therewith, wherein the impeller overlies themotor housing such that the motor housing is positioned between theimpeller and the entrance to the inlet.
 2. The system according to claim1, wherein an interior surface of the compressor housing extends aroundthe central cavity, and wherein the motor housing is spaced away fromthe interior surface, such that air may flow around the motor housing todissipate heat generated by the motor.
 3. The system according to claim1, wherein the compressor housing is a monolithic housing.
 4. The systemaccording to claim 1, further comprising an outer envelope configured toretain a lift gas therein and an inner envelope disposed within theouter envelope, the inner envelope being configured to retain ballastgas therein, wherein the compressor assembly regulates an amount of airwithin the inner envelope.
 5. The system according to claim 1, furthercomprising an outer envelope configured to retail a ballast gas therein,and an inner envelope disposed within the outer envelope and configuredto retain a lift gas therein, wherein the compressor assembly regulatesan amount of air within the outer envelope.
 6. The system according toclaim 1, further comprising a valve assembly coupled to the inlet, thevalve assembly being configured to regulate an amount of air enteringinto the entrance of the inlet.
 7. A system comprising: an altitudecontrol system for an unmanned aerial vehicle comprising: a compressorassembly including: a compressor housing comprised of a first materialhaving a first coefficient of thermal expansion (“CTE”); a rotatingshaft assembly coupled to the compressor housing and including: adriveshaft comprised of a second material having a second CTE; and abearing assembly coupled to the driveshaft, the bearing assemblyincluding an interior race extending around the driveshaft and a distalrace extending around and spaced apart from the interior ring; anaxially movable bearing carrier housing the bearing assembly, thebearing carrier including a first upper portion, a second lower portion,and an intermediate projection therebetween; a motor coupled to therotating shaft assembly; and a biasing element coupled to the bearingcarrier and configured to bias the bearing carrier toward the bearingassembly so as to preload the bearing assembly; and an envelopeconfigured to retain a ballast gas therein, wherein the compressorassembly is configured to regulate an amount of air within the envelope,and wherein the first CTE and the second CTE are different such that thefirst material is configured to expand at a rate that is different thanthe second material as ambient temperature changes.
 8. The systemaccording to claim 7, wherein when the biasing element is configured tobias the bearing carrier, the bearing carrier is configured to move thedistal ring of the bearing assembly in an axial direction.
 9. The systemaccording to claim 7, wherein the bearing assembly further includes aplurality of ball bearings positioned between the interior and distalraces.
 10. The system according to claim 7, wherein the compressorassembly further includes an inlet extending through the compressorassembly, the system further comprising a valve assembly coupled to theinlet, the valve assembly being configured to regulate the amount of airentering into the inlet.
 11. A system comprising: an altitude controlsystem for an unmanned aerial vehicle comprising: a compressor assemblycomprising: a compressor housing comprised of a first material having afirst coefficient of thermal expansion (“CTE”); a rotating driveshaftcoupled to the compressor housing, the rotating driveshaft comprised ofa second material having a second CTE; a bearing assembly coupled to thedriveshaft, the bearing assembly including an interior race extendingaround the driveshaft, a distal race extending around and spaced apartfrom the interior race by ball bearings positioned between the interiorand distal races; and a preloading mechanism configured to dynamicallycompensate for differences in the first CTE and second CTE throughout aflight of the unmanned aerial vehicle by continually changing apreloading force applied to the bearing assembly.
 12. The systemaccording to claim 11, wherein the preloading mechanism includes: amovable bearing carrier underlying the bearing assembly and movablealong an axis parallel to the rotating driveshaft; and a springconfigured to bias the bearing carrier towards the bearing assembly. 13.The system according to claim 12, wherein when the spring biases thebearing carrier, the bearing carrier is configured to move the distalrace of the bearing assembly.
 14. A system comprising: an altitudecontrol system for an unmanned aerial vehicle comprising: an inletopening to an interior portion of the unmanned aerial vehicle, the inletopening having a circumferential area; a valve assembly coupled to theinlet opening including: a valve head configured to move into and awayfrom the inlet opening so as to change a size of the circumferentialarea of the inlet opening; a driveshaft coupled to the valve head at afirst end; and a motor assembly coupled to a second end of thedriveshaft, wherein the valve head is configured to move between a firstfully extended position within the inlet opening and a second retractedposition away from the inlet opening, and wherein when the valve head isin the first fully extended position, the valve head is arranged tooccupy an entire circumferential area of the inlet opening therebyprohibiting free flow of contents into and out of the inlet opening. 15.The system according to claim 14, wherein the motor assembly furthercomprises a motor and a motor housing, the motor housing defining a boreconfigured to receive the driveshaft of the motor therethrough.
 16. Thesystem according to claim 15, wherein the motor housing further includesan explosion proof shaft seal disposed in the bore and mounted on thedriveshaft of the motor.
 17. The system according to claim 15, whereinthe motor housing further includes a flame arrestor.
 18. A system for anunmanned aerial vehicle comprising: an altitude control systemcomprising: a compressor assembly including: a compressor housingincluding an inlet, an outlet, and a central cavity extendingtherethrough and joining the inlet to the outlet; a diffuser coupled tothe compressor housing; a motor housing disposed within the centralcavity at the inlet of the compressor housing; a motor disposed withinthe motor housing; and an impeller disposed within the compressorhousing and coupled to a compressor driveshaft for rotation therewith;and a valve assembly coupled to an inlet opening of the inlet of thecompressor including: a valve head configured to move into and away fromthe inlet opening so as to change a size of a circumferential area ofthe inlet opening; a valve driveshaft coupled to the valve head at afirst end; and a motor assembly coupled to a second end of thedriveshaft, wherein the valve head is configured to move between a firstfully extended position within the inlet opening and a second retractedposition away from the inlet opening, and wherein when the valve head isin the first fully extended position, the valve head is configured tooccupy an entire circumferential area of the inlet opening and therebyprohibit free flow of contents into and out of the inlet opening. 19.The system according to claim 18, wherein the compressor assemblyfurther comprises: a rotating shaft assembly that includes thecompressor driveshaft, the rotating shaft assembly further including: abearing assembly coupled to the compressor driveshaft, the bearingassembly including an interior race extending around the driveshaft anda distal race extending around and spaced apart from the interior ring;and a movable bearing carrier that houses the bearing assembly; a motorcoupled to the rotating shaft assembly; and a biasing element coupled tothe bearing carrier and configured to bias the bearing carrier so as topreload the bearing assembly.
 20. The system according to claim 18,wherein the altitude control system further comprises an electronicscontrol assembly including a circuit board including a processorconfigured to control the compressor assembly.